The purpose of gait analysis is to quantify a person's walking pattern and the neuromuscular strategies the body uses to produce the observed movement. A computerized video camera system measures the movement pattern, and special platforms built into the floor measure forces acting on the feet. From the measured movements and forces, the mechanical work done by the body during walking can be estimated Current techniques used to approximate work oversimplify the model of the body and its movements and introduce errors into the estimates. Our research is investigating more complex models of the body to learn how these models affect mechanical work estimates. One study of 10 normal subjects that examined the work done at the ankle joint during gait has been published. The study employed a more sophisticated model of the ankle joint and included additional terms, previously ignored, in the mechanical work calculations. Data from another study, which examined the mechanical work done at the knee joint, have been completed and presented. A third study involving 15 subjects produced a dramatically improved model of the foot. A study currently under way is investigating the effect of dramatically different speeds on the mechanics of walking. It is hypothesized that two modes of walking exist rather than a continuum of a single walking strategy. A final study, which is near completion, evaluate a new technique for determining the role each major muscle group of the lower extremity plays in providing support to and propulsion of the body during walking. The results of these studies suggest that a complete and numerically consistent mechanical characterization of human movement is feasible. The application of these analytic techniques to the evaluation of human motion will have implications for rehabilitation and surgical treatment in patient populations.